The present invention relates to brake control systems and pertains particularly to a brake control system having a retarding mode of operation.
Heavy material-carrying vehicles which must travel down long, steep grades have brake-retarding requirements which are distinct from the relatively infrequent service braking needs. For instance, it is normal to establish a preselected intermediate setting of the brakes during a downhill run for retarding, but such condition results in the necessity for absorbing a considerable amount of energy in the individual brakes for a relatively long period of time. This energy must be efficiently dissipated in order to increase the service life of the brakes and prevent early brake failure.
Sophisticated oil-cooled, disc-type brakes with associated cooling systems are being developed by the industry to accomplish this dissipation of energy. In contrast, service braking requirements are usually intermittent and less total energy is thereby absorbed. But service braking has a greater need than retarding for emergency maximum energy absorption. These factors indicate a need for separate retarding control and the possibility of differentially sizing the brake sets and their cooling capacities at the front and rear of the vehicle.
Another safety factor should also be considered with tractor-trailer combination vehicles. With service braking, for example, it is desirable to either delay the application of the brakes at the front of the vehicle with respect to the rear or to generally absorb similar amounts of energy at both locations. Such action will generally avoid a relatively dangerous condition known as jackknifing, wherein the heavier trailing portion of the vehicle tends to overrun the otherwise more quickly decelerating forward portion. On the other hand, retarding requirements are generally not as severe in this regard. It is therefore desirable to consider these safety parameters along with the other abovementioned factors to provide a control system that differentially apportions energy absorption to the front and rear sets of brakes in a manner which more effectively and economically matches these sets of brakes and their associated cooling systems.